Re-take - Useful Information for 2394 :

[amberleaf]

Taken from Extracts
You have to put in the studying

GN-3 : P/35
Method 2 . ( R[SUP]2[/SUP] ) Testing bonding conductors & earthing conductors

re-cap ,
To confirm the continuity of these protective conductor's , test method 2 may be used .
This method can also be used to confirm a bonding connection between extraneous-conductive-part , where it is not possible to see a bonding-connection e.g.

P/34
Test method 2 ... ( for circuit )
re-cap ,
This test measures the continuity résistance of the circuit protective conductor , ( R[SUP]2[/SUP] ) which should be recorded on a , Schedule of Test Results
( see earlier note " Parallel earth parts & effects on test readings )

P/32 , 2.7.5. Continuity of protective conductors , including Main & Supplementary bonding

Regulation 411.3.1.1. requires that installations which provide protection against electric-shock using ( ADS ) must have a circuit protective conductor ( run ) to & terminated at each point in the wiring & each accessory , refer .
Regulation 612.2.1. requires that a continuity check be carried out on all circuits including ring-circuit's
There are ( Two widely used test methods ) that have evolved for checking conductor continuity , also measures ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) which , when added to the external impedance ( Ze ) enables the earth fault loop impedance ( Zs ) to be checked against the design

P/33 , Test method 1 ... ( for circuit ) Connections for testing continuity of protective-conductors

2.7.6. Continuity of ring-final-circuit-conductor(s)
Three-steps test is required to ( Verify the continuity ) Etc refer
Regulation 612.2.2.

 

[amberleaf]

My point is :

in your wording in Exams . You have proven a true reading . ( Ω ) in the eyes of C&Gs

I normally , Null my test-leads when carrying out the ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) test ... meter takes the résistance of the leads into consideration Let you examiner known . ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) You have proven a true reading . " Nulling out leads "

 

[amberleaf]

Why do you need to null the test leads on an instrument , in the eyes of C&Gs

Accuracy. If you don't null ( zero ) the test leads when you measure the résistance of your circuit you will also be measuring the resistance of your leads at the same time giving a false / inaccurate


Functional check of your leads & tester

 

[amberleaf]

On Rant Mode :

There was also evidence of a lack of understanding of basic electrical principles . RCDs

Chief Examiners’ report - August 2013

A large number of candidates were unable to correctly explain the effect on an RCD of a line to neutral fault. Most candidates believed this would result in the operation of the RCD and very few identified that the RCD would operate in the event of a fault between live conductors & earth.

Most candidates identified the Electricity at Work Regulations as identifying the requirements for an inspector (although some incorrectly referred to it as an Act). Very few candidates were able to identify the title given to an inspector (Duty Holder) and the status (competent person) which are attributed to the Inspector in EWR.

▼▼▼
Candidates appear to be unaware of the required action by the inspector in the event of a dangerous situation being discovered during the inspection. The most common incorrect answer was to isolate the supply, often including repair the fault etc. The inspector’s responsibility is referred to in GN-3 under Item 1.2 Required competence as: ‘In the event of a dangerous situation being found the inspector should recommend the immediate isolation of the defective part.’ It is important to remember that the inspector must obtain permission before isolating to ensure there are no other serious consequences to that action

Chief Examiners’ report . There's always room for Improvement .

GN-3 . 1.2 Required competence .

610.5. The inspector carrying out the inspection & testing or any electrical installation must as appropriate to his or her function , have a sound knowledge & experience relevant to the nature of the installation being inspected & tested , & of BS-7671: & other relevant technical standards , The inspector must also be fully versed in the inspection & testing procedures & employ suitable test equipment during the inspection & testing process .

The inspector should have sufficient inspection & testing skills together with experience in interpreting the results with respect to the requirements of BS-7671:

it is worth noting that the person responsible for inspection & testing may be required to formally demonstrate competence by means of registration / certification under a recognised scheme . etc

it is the responsibility of the inspector , as appropriate to either the initial or periodic inspection , to

634.2. ►► In the event of a dangerous situation being ( found ) the inspector should recommend the , immediate isolation of the defective part .
The person ordering the work should be informed , in writing , of this recommendation without delay .

 

[Meggerman]

634.2. ►► In the event of a dangerous situation being ( found ) the inspector should recommend the , immediate isolation of the defective part .
The person ordering the work should be informed , in writing , of this recommendation without delay .[/QUOTE]
mmm.... and then when they don't do anything about it, who are they going to look at. I would still isolate it myself if it was not a easy fix. I could quite happily argue about that as could justify my actions on grounds of safety. If they want it back on in an unsafe condition let them turn it back on.

 

[amberleaf]

Meggerman . I do understand your views .

634.2. ►► In the event of a dangerous situation being ( found ) the inspector should recommend the , immediate isolation of the defective part .
The person ordering the work should be informed , in writing , of this recommendation without delay .

It is important to remember that the inspector must obtain permission before isolating to ensure there are no other serious consequences to that action

Meggerman , My situation here is only to point out the facts here .

 

[Meggerman]

Meggerman . I do understand your views .

634.2. ►► In the event of a dangerous situation being ( found ) the inspector should recommend the , immediate isolation of the defective part .
The person ordering the work should be informed , in writing , of this recommendation without delay .

It is important to remember that the inspector must obtain permission before isolating to ensure there are no other serious consequences to that action

Meggerman , My situation here is only to point out the facts here .

I know mate, I'm not shooting the messenger . I think 634.2. should be rewritten with regard to domestic (as there is going to be nothing of more serious consequence in a home than that of electric shock or fire) and give Electricians the authority to isolate dangerous situations as Gas Safe engineers can.

 

[amberleaf]

100% right my friend . Electricians the authority to isolate dangerous situations as Gas Safe engineers can.

 

[amberleaf]

On Rant mode .

( IR ) GN-3 : The purpose of the insulation résistance test is to verify that the insulation of conductors provides adequate insulation .
is not damaged & that live conductors or protective conductors are not short-circuited .

( IR ) -&-s . That any circuit under ( 2MΩ ) should be investigated

GN-3 are reminding us . résistance values should be ( 2MΩ or greater ) for each circuit .
The whole installation must have an ( IR ) résistance of greater than ( 1MΩ )

Table 61 : Minimum values of ( IR ) 1.0MΩ
Note 2 : ( IR ) values are usually much higher than those of Table 61 . 1.0MΩ

My reason is ( Conductors in Parallel ) " Scenario "
( Zdb ) Three phase sub-main is tested & the results are ??

L1 to earth - 130MΩ
L2 to earth - 80MΩ
L3 to earth - 50MΩ
Neutral to earth - 100MΩ

Conductors joined & tested to earth . ( 500V - d.c. )

Calculation : 1/R[SUP]1 [/SUP] + 1/R[SUP]2 [/SUP]+ 1/R[SUP]3 [/SUP]+ 1/R[SUP]4 [/SUP]= 1/Rt
Values :- 1/30 + 1/80 + 1/50 + 1/100 + 1/0.05 = 19.92MΩ

By Calculation : 130 X[SUP]1 [/SUP] + 80 X[SUP]1 [/SUP] + 50 X[SUP]1 [/SUP] + 100 X[SUP]1 [/SUP] = X[SUP]1 [/SUP]19.92MΩ

lower because the conductors are in ( Parallel )

GN-3 : reminds us . Testing of individual circuits . New & Existing circuit's.

Extracts : GN-3 :
( IR ) Simple installations that contain No distribution circuits should preferably be tested as a Whole .

To perform the test in a complex installation it may need to be ( subdivided ) into its component parts .

reminder : 2392 / 2394 :
Although an ( IR ) value of Not less than ( 1MΩ ) complies with Regulation , New installations should Not yield test results this ( LOW )

Regulation : Note 2 : ( IR ) values are usually much higher than those of Table 61 . 1.0MΩ

 

[GLENNSPARK]

634.2. ►► In the event of a dangerous situation being ( found ) the inspector should recommend the , immediate isolation of the defective part .
The person ordering the work should be informed , in writing , of this recommendation without delay .

mmm.... and then when they don't do anything about it, who are they going to look at. I would still isolate it myself if it was not a easy fix. I could quite happily argue about that as could justify my actions on grounds of safety. If they want it back on in an unsafe condition let them turn it back on.[/QUOTE]


without first gaining permission from the person ordering the work?

 

[amberleaf]

On rant mode :

Table 41.5. ( Zs ) non-delayed RCDs
BS-EN-61008-1
BS-EN-61009-1

BS-7671:2011: gives maximum earth fault loop impedance permissible for the correct operation of RCD

The values . By calculation
50 ) is the maximum voltage
I∆n ) is the trip rating of the residual current device .
Zs ) is the earth fault loop impedance

rating of the device is ( 100mA ) .. 50 / 01 = 500Ω

Electrode résistance in ( Ω ) 100mA - 500Ω

P/57 . BS-7671: Note 2* , The résistance of the installation earth-electrode should be low as practicable .
A value exceeding 200 ohms may not be stable .

( 50V ÷ 30mA = 1.666666667 ) 1667*

411.5. TT system
411.5.1. Every exposed-conductive-part which is to be protected by a single protective device shall be connected , via the main earthing terminal , to a common earth-electrode .

GN-3 P/48 . E1
Scenario : Three electrodes - earthing electrode under test . a current electrode & a potential electrode .
measurement taken , 79Ω , 85Ω , 80Ω . = 244 ... added together & an average value calculated . 244 ÷ 3 = 81.33Ω

find the different between the average value & the highest measured value . ( 85Ω ) 85 sub 81.33 = 3.67

the percentage of this value to the average value must now be found . 3.67 x 100 ÷ 81.33 = 4.51

fig 2.7 . P/49
GN-3 tells us that the accuracy of this measurement is typically ( 1.2 times the percentage deviation )
correct value . x percentage deviation ( 1.2 ) 4.51 x 1.2 = 5.41

refer to . P49
The accuracy of the measurement using this technique is typically ( 1.2 times ) the percentage deviation of the readings , it is difficult to achieve an accuracy of measurement better than ( 2% ) & inadvisable to accept readings that differ by more than ( 5% ) refer .

 

[Sintra]

Guys can we please keep this thread as info only from Amberleaf and cut the replies.

 

[amberleaf]

Extracts'

After replacing a consumer unit, it is found that there is a shared neutral between the upstairs and downstairs lighting circuits.
Would it comply with BS-7671: if I put the lighting onto one circuit to avoid the RCD tripping ?

Electrical Safety First's Best Practice Guide No 6 ( Consumer unit replacement in domestic premises ) sets out a procedure to help avoid such foreseeable circumstances.

In any event, the shared neutral situation must be corrected to remove the electric shock hazard.

Preferably each circuit should be provided with its own neutral to satisfy Section 314.

However, where this is not practicable, the two lighting circuits sharing the neutral may be connected to a single protective device (creating a single circuit), provided that the circuit is suitable for the connected load.

Regulation number(s) 314 .

 

[amberleaf]

just in from work . knock something up .
On rant mode .

Circuit breakers : As it cannot be predicted where in the ( Range ) a circuit breaker will trip ?? 3 / 5 , 5 / 10 , 10 / 20 . etc
3 x 32A = 96.
5 x 32A = 160.
10 x 32A = 320
The limiting values of earth fault loop impedance for BS-EN-60898-1 , in Table 41.3 are based on the upper range values of current

Instantaneous Tripping .

B above ( 3 In ) up to & including ( 5 In )
C above ( 5 In ) up to & including ( 10 In )
D above ( 10 In ) up to & including ( 20 In )

P/301 , fig 3A4 . The prospective earth fault current for ( 32A type B ) circuit breaker is required to be not less than ( 160A ) .. that is , 5 In . etc
by calculation 5 x 32A = 160A .. Zs ≤ 230 / 160 = 1.43 . etc
P/302 , fig 3A5 . The prospective earth fault current for ( 32A type C ) circuit breaker is required to be not less than ( 320A ) .. that is , 10 In . etc
by calculation 10 x 32A = 320A
P/303 , fig 3A6 . The prospective earth fault current for ( 32A type D ) circuit breaker is required to be not less than ( 640A ) .. that is , 20 In . etc
by calculation 20 x 32A = 640A
Type B trips between 3 & 5 time full load current .. ( 5 maximum ) etc
Type C trips between 5 & 10 times full load current
Type D trips between 10 & 20 times full load current.

Confirm the maximum permitted earth fault loop impedance of BS-EN-60898-1 , circuit breakers
Type B circuit-breaker will withstand currents of upto a maximum of ( 5x ) it's current rating ( In ) before disconnection occurs.

Divide nominal voltage to Earth ( Uo ) 230 by ( 5 ) 230 ÷ 5 = 46.

Type C, the maximum ( 10x ) current rating 230 / 10 = 23.

Type D, maximum ( 20x ) current rating 230 / 20 = 11.5

32A type B circuit breaker ( ÷ ) B figure of ( 46 ) by calculation :- 46 ÷ 32 = 1.43, rounded up to 1.44 which is the value given in table 41.3 of BS- 7671.

To adjust the value for the temperature corrected value, multiply ( 1.44 ) figure in this instance by 0.8 which gives us 1.44 x 0.8 = 1.152 , value given in O.S.G. table B6 ( B 32A - 1.16 )

 

[amberleaf]

Initial Verification . is required for ( New work ) & alterations & additions .

Cover your " Derriere "

GN-3 . P/16 . ( Verification ) as a Competent person .
The responsibility for comparing Inspection & Test-results with relevant criteria , as required by Regulation 612.1. lies with the party responsible for inspection & testing the installation , this party , which may be the person carrying out the inspection & testing , should sign the inspection & testing box of the ( EIC ) or the declaration box of the ( MEIWC ) if the person carrying out the inspection & testing has also been responsible for the design & construction of the installation , he or she must also sign the design & construction boxes of the ( EIC ) , or make use of the single signature ( EIC )

Initial Verification
Q/As C&G. State the reason why it is necessary to undertake an initial verification !!

GN-3 . P/15 . 2.1. ( Initial Verification ) is carried out on a ( New installation ) before it is put into service .
The ( Purpose of initial verification ) is to confirm by way of Inspection & testing , during construction & on completion , that the installation complies with the design & construction aspects of BS-7671: .. in so far as is reasonably practicable .

612 Testing .
612.1. The tests of Regulations 612.2. to 612.13 , where relevant , shall be carried out & the results compared with relevant criteria

610.1. Initial Verification
Every installation shall , during erection & on completion before being put into service , be inspected & tested to verify , .. in so far as is reasonably practicable

Protection of persons & livestock
The prevention of damage to property & installed equipment , during inspection & testing .

611.2. The inspector shall be made to verify that the installed electrical equipment is . refer (i) (ii) (iii) etc
GN-3 : 611.2. BS-7671: provides a format list in Regulation 611.2. of item to be ( Verified ) again so far as is reasonably

612 Testing .
612.1. The tests of Regulations 612.2. to 612.13 , where relevant , shall be carried out & the results compared with relevant criteria , (i) (ii) (iii) etc